Gender variation inSilene acaulis (Caryophyllaceae)

Abstract

Silene acaulis (Caryophyllaceae) is an alpine-arctic plant with a gynodioecious breeding system, but significant variation in sex expression has been reported. In addition, population sex ratio may be modified by the anther-smutMicrobotryum violaceum (Pers.)Deml & Oberwinkler, which sterilizes individuals of both sexes. A survey was undertaken at several sites on Baffin Island, Canada, to determine sex ratio and assess variation in female function among morphologically hermaphroditic individuals. The degree of anthersmut infection was also measured. Six sites had high female frequencies ranging from 72–80% and < 2% smut infection. High female frequencies may indicate cytoplasmic control of male-sterility. A seventh site from a mesic habitat had only 50% females and a higher rate of smut infection (22%). Of the three sites studied in detail, 84% of females set at least one capsule compared to only 25% of the hermaphrodites, indicating reduced female function. Hermaphrodites displayed significant variability in female function. Flowers with short styles (< 4.0mm) had degenerated ovules, and field estimates confirmed that only 5% of these individuals set capsules, but comprised the majority (> 55%) of hermaphrodites. Although hermaphrodites with short-styled flowers functioned solely as males, there was no increase in pollen production compared to long-styled hermaphrodites. Long-styled hermaphrodites produced the same number of ovules as females, and all set at least one capsule but these plants were uncommon (< 11%) at all sites.